The present invention relates to a process for preparing a quinolylacrylonitrile derivative from a quinolinecarbaldehyde derivative. The quinolylacrylonitrile derivative produced by the method of the invention is employable as a starting compound for the preparation of a quinolylpropenal derivative which is utilizable for the synthesis of a cholesterol reducing agent (HMG-CoA reductase inhibitor).
Until now, it has been known that the quinolylpropenal derivative is prepared by the two step process comprising a step of reducing a quinoline acrylate by diisobutylaluminum hydride to give quinolylpropenol and a subsequent step of oxidizing the quinolylpropenol by the use of a combination of oxalyl chloride and dimethylsulfoxide, or manganese dioxide (J. Med. Chem., 34, 367 (1991)).
Further known is a method of selectively reducing the cyano group to a formyl group by the use of a diisobutylaluminum hydride reducing agent, keeping the double bond of an acrylonitrile compound to produce a propenal compound (Heterocycles, 29, 691(1989)).
Both of the above-mentioned process and method are disadvantageous from the viewpoint of industrial preparation because these process and method utilize iisobutylaluminum hydride or manganese dioxide which requires careful handling procedures and complicated post-treatment.
The present invention resides in a process for preparing 3-[2-cyclopropyl-4-(4-fluorophenyl)-3-quinolyl]-prop-2-enenitrile which comprises the steps of reacting 2-cyclopropyl-4-(4-fluorophenyl)quinoline-3-carbaldehyde with acetonitrile in the presence of a base to produce a mixture of 3-[2-cyclopropyl-4-(4-fluorophenyl)-3-quinolyl]prop-2-enenitrile and 3-[2-cyclopropyl-4-(4-fluoro-phenyl)quinolin-3-yl]-3-hydroxypropionitrile; and dehydrating the mixture in the presence of a dehydrating agent.
The starting compound of the reaction of the invention, that is, 2-cyclopropyl-4-(4-fluorophenyl)quinoline-3-carbaldehyde [hereinafter referred to as quinolinecarbaldehyde derivative], the intermediate product, that is, 3-[2-cyclopropyl-4-(4-fluorophenyl)quinolin-3-yl]-3-hydroxypropionitrile [hereinafter referred to as quinolylhydroxypropionitrile derivative], and the desired compound, that is, 3-[2-cyclopropyl-4-(4-fluorophenyl)-3-quinolyl]prop-2-enenitrile [hereinafter referred to as quinolylacrylonitrile derivative] are the compounds represented, respectively, by the following formulas (1), (2), and (3): 
The invention further resides in the above-mentioned 3-[2-cyclopropyl-4-(4-fluorophenyl)-3-quinolin-3-yl]-3-hydroxypropionitrile.
The invention furthermore resides in a process for preparing 3-[2-cyclopropyl-4-(4-fluorophenyl)-3-quinol-yl]prop-2-enenitrile which comprises the steps of reacting 2-cyclopropyl-4-(4-fluorophenyl)quinoline-3-carbaldehyde with acetonitrile in the presence of a base; and dehydrating the resulting product in the presence of a dehydrating agent.
The invention furthermore resides in a method for preparing 3-[2-cyclopropyl-4-(4-fluorophenyl)-3-quinolyl]prop-2-enenitrile which comprises reacting 2-cyclopropyl-4-(4-fluorophenyl)quinoline-3-carbaldehyde with acetonitrile in an organic solvent in the presence of a base.
The quinolylacrylonitrile derivative of the formula (3) {i.e., 3-[2-cyclopropyl-4-(4-fluorophenyl)-3-quinolyl]prop-2-enenitrile} obtained by the invention can be converted into 3-[2-cyclopropyl-4-(4-fluorophenyl)-3-quinolyl]prop-2-enal by reducing the derivative using a Raney-nickel in the presence of a combination of formic acid and water [in an amount of 0.25 to 1 volume part per one volume part of the formic acid].
The 2-cyclopropyl-4-(4-fluorophenyl)quinoline-3-carbaldehyde of the formula (1) which is the starting material of the reaction of the invention is described in JP-A-1-279866, EP-A-304063, and U.S. Pat. No. 5,011,930, and is already known.
Examples of the bases employed in the reaction of the invention include a metal hydride such as lithium hydride, sodium hydride, potassium hydride, or calcium hydride; a metal amide such as lithium amide, sodium amide, lithium diisopropylamide, lithium bis(trimethylsilyl)amide, or potassium bis(trimethylsilyl)amide; a metal alkoxide such as sodium methoxide, sodium ethoxide, sodium t-butoxide, potassium t-butoxide, magnesium methoxide, or magnesium ethoxide; an alkyl lithium such as methyllithium, butyllithium, or t-butyllithium; or a metal hydroxide such as lithium hydroxide, sodium hydroxide, potassium hydroxide, or calcium hydroxide. Preferred are a metal hydride, a metal alkoxide, and a metal hydroxide. More preferred are a metal hydride and a metal alkoxide.
The base is employed in an amount of preferably 0.9 to 3.0 moles, more preferably 1.0 to 2.0 moles, per one mole of the starting compound, i.e., the quinolinecarbaldehyde derivative.
In the reaction, the acetonitrile is employed in an amount of preferably 0.9 to 100 moles, more preferably 1.0 to 60 moles, per one mole of the starting compound, i.e., the quinolinecarbaldehyde derivative.
In the reaction, the dehydrating agent functions to dehydrate the below-mentioned quinolylhydroxypropionitrile derivative having a hydroxyl group which is probably produced in the reaction as an intermediate product to give the desired product [quinolylacrylonitrile derivative having a double bond] according to the below-illustrated reaction (4): 
Examples of the dehydrating agents include inorganic acids such as hydrochloric acid and sulfuric acid; organic acids such as formic acid, acetic acid, and trifluoroacetic acid; organic acid esters such as methyl formate, ethyl formate, propyl formate, butyl formate, and ethyl acetate; amides such as N,N-dimethylformamide; organic acid anhydrides such as acetic anhydride and trifluoroacetic anhydride; acid chlorides such as mesyl chloride, thionyl chloride, and acetyl chloride; tertiary amines such as trimethylamine, triethylamine, ethyldiisopropylamine, diethylisopropylamine, and benzyldimethylamine; and silane compounds such as 1,1,1,3,3,3-hexamethyldisilazane. Preferred are organic acid esters and a combination of an acid chloride and a tertiary amine. More preferred are organic acid esters. Most preferred are formic acid esters. The dehydrating agent is employed in an amount of preferably 0.1 to 100 moles, more preferably 0.2 to 50 moles per one mole of the starting compound, i.e., the quinolinecarbaldehyde derivative.
The reaction of the invention can be carried out by reacting the quinolinecarbaldehyde derivative and acetonitrile in the presence of a base to produce a mixture of the quinolylhydroxypropionitrile derivative (intermediate product) and the quinolylacrylonitrile derivative (desired product), and completing the reaction upon addition of a dehydrating agent at an atmospheric pressure or an increased pressure. The reaction temperature is in the range of, preferably, xe2x88x9278xc2x0 C. to 80xc2x0 C., more preferably xe2x88x9230xc2x0 C. to 50xc2x0 C.
The reaction of the starting compounds (guinolinecarbaldehyde derivative and acetonitrile) in the presence of a base can be carried out in an organic solvent to produce directly (this means xe2x80x9cwithout utilizing a dehydrating agentxe2x80x9d) the desired product. The organic solvent is one other than the acetonitrile.
The organic solvent preferably has a dielectric constant of 10 or less in the temperature range of 20 to 25xc2x0 C. (at an optionally selected temperature in this range). The details of xe2x80x9cdielectric constantxe2x80x9d are described in xe2x80x9cChemistry Handbook, Basic Issue, 4th edition (II)xe2x80x9d (Maruzen Publishing), and xe2x80x9cSolvent Handbook, 1st editionxe2x80x9d (Kodansha Scientific). Examples of the organic solvents include aliphatic solvents such as hexane, heptane, cyclohexane, methylene chloride, chloroform, and carbon tetrachloride; aromatic solvents such as benzene, toluene, xylene, chlorobenzene and dichlorobenzene; and ether solvents such as methylal, tetrahydrofuran, and dioxane. Preferred are aromatic solvents and ether solvents. More preferred are aromatic solvents. Most preferred is toluene. The organic solvents can be employed singly or in combination.
The organic solvent can be employed in an amount of preferably 0.5 to 50 weight parts, more preferably 1 to 20 weight parts, per one weight part of the quinolinecarbaldehyde derivative (starting compound).
The reaction can be carried out by reacting the quinolinecarbaldehyde derivative and acetonitrile at an atmospheric pressure or an increased pressure in an organic solvent in the presence of a base. The reaction temperature is in the range of preferably 30 to 140xc2x0 C., more preferably 40 to 120xc2x0 C.
In the reaction utilizing an organic solvent, the base is employed in an amount of preferably 0.5 to 3.0 moles, more preferably 0.8 to 2.0 moles, per one mole of the quinolinecarbaldehyde derivative. (starting compound).
In the reaction utilizing an organic solvent, acetonitrile is employed in an amount of preferably 0.9 to 50 moles, more preferably 1.0 to 30 moles, per one mole of the quinolinecarbaldehyde derivative (starting compound). The reaction product (desired product) of the reactions of the invention, that is, quinolylacrylonitrile derivative can be isolated and purified after the reaction is complete, by a conventional procedure such as recrystallization or column chromatography.